Circuits for discharging a capacitor through an arc discharge device



Sept. 20, 1966 a. E. TOMPKINS 3,274,439

CIRCUITS FDR DISCHARGING A CAPACITOR THROUGH AN ARC DISCHARGE DEVICE Filed 001;. 30, 1961 22 16' 7, f m Z6 14 1a [2 Phfi W1 26 v 5! 52 F 1Q g 50 Z 3a IN VE NTOR. fl/PA/A AFD 5 75MPm/s United States Patent F 3,274,439 CIRCUITS FUR DiStIHAlRGiNG A CAPACETQR THROUGH AN ARC DISCHARGE DEVHIE Brainard E. Tompkins, Yardviiie, NJ assignor to Radio Corporation of America, a corporation of lDeiaware Fiied Get. 30, 1961, Ser. No. l i-3,339 9 (llaims. (Cl. 315237) This invention relates generally to discharge circuits, and more particularly to improved circuits for discharging a relatively large capacitor through a load. The improved discharge circuits of the present invention are particularly useful for energizing loads with relatively large pulses of energy by means of switching devices of relatively low power-handling capacity.

It has been proposed to discharge a capacitor through a load, such as an arc discharge device, by connecting the arc discharge device in series with a thyratron and the capacitor. The capacitor is usually charged to a voltage that is just below the break-down voltage of the are discharge device by a power supply, and then discharged through the arc discharge device by triggering the thyratron into a conductive state. The amount of energy capable of passing through the arc discharge device is limited by the current-handling capacity of the thyratron, the current passing through the arc discharge device being the same current that passes through the thyratron. Thus, where it is necessary to energize an arc discharge device with current from an extremely large capacitor, either a thyratron of high energy-handling capacity or an ignitron is necessary. High energy-handling thyratrons and ignitrons, however, are relatively expensive, bulky, and inconvenient to use.

It has also been proposed to trigger an arc discharge device into conduction with a pulse from a transformer whose Winding surrounds the envelope which contains the gas of the discharge device. While a capacitor can be discharged through the arc discharge device when so triggered, the triggering time is relatively erratic and indefinite, making this triggering means unsuitable for certain applications.

It is an object of the present invention to provide an improved circuit for discharging a relatively large capacitor through a load by using low powered switching means to initiate conduction through the load.

It is another object of the present invention to provide an improved circuit for switching relatively high energy through an arc discharge device by means of a thyratron of relatively low power capacity.

Still another object of the present invention is to provide an improved circuit for discharging a capacitor through a load wherein the only limitation to the flow of current is provided by the load alone.

A further object of the present invention is to provide an improved circuit for discharging a capacitor through an arc discharge device, employing a power supply whose output voltage is smaller than the break-down voltage of the arc discharge device.

Still a iurther object of the present invention is to provide an improved circuit of the type described that is relatively simple in structure and operation, economical to build, and highly reliable in use.

In accordance with the present invention, the novel discharge circuits comprise a relatively large capacitor connected to a power supply to be charged thereby. A load, in the form of an arc discharge device, for example, is connected across the capacitor by low resistance leads. The capacitor is charged to a voltage below the breakdown voltage of the arc discharge device. Switching means are provided to apply a triggering voltage to one of the terminals of the arc discharge device to trigger it into conduction. The rise time of the triggering pulse 3,274,439 Patented Sept. 2%, 1966 is extremely fast, and the inductive reactance produced in the low resistance lead between the capacitor and the arc discharge device permits the triggering pulse to add to the voltage on the capacitor, whereby to trigger the are dis charge device into conduction. The current through the arc discharge device is limited only by the arc discharge device and leads connecting it to the capacitor. A device requiring a large amount of current to operate can be inserted in series with the capacitor and the arc discharge device. Thus, certain metals, for example, may be inserted in the discharge circuit to evaporate or to explode the metals when a large pulse of current is sent through them.

The novel features of the present invention, both as to its organization and methods of operation, as well as additional objects and advantages thereof, will be more readily understood from the following description, when read in connection with the accompanying drawing, in which similar reference numbers refer to similar components, and in which:

FIG. 1 is a schematic diagram of an improved discharge circuit in accordance with the present invention, and employing one power supply;

FIG. 2 is a schematic drawing of another discharge circuit in accordance with the present invention, and employing one or two power supplies; and

FIG. 3 is a schematic diagram of a portion of the schematic diagram of FIG. 2, showing an .additional load in the high energy discharge circuit.

Referring, now, to FIG. 1, there is shown a discharge circuit 10 for discharging a capacitor 12 through an arc discharge device 141, such as a flash lamp, a spark gap, or a laser device, for example. The capacitor 12 may be one with a relatively large capacity, or may represent a bank of capacitors connected in parallel, for supplying the arc discharge device 14 with a large pulse of energy.

The capacitor 12 is connected in shunt with a resistor 18 of a voltage divider comprising serially connected resistors 16, 18, and 20. The resistor 16 is connected to the positive output terminal 22 of a source of voltage from a unidirectional power supply (not shown). One end of the resistor 20 is connected to a common connection, such as ground, to which the negative output terminal 24 of the power supply is also connected. The capacitor 12 is connected between terminals 26 and 28 of the arc discharge device 14 by leads 37 and 39 of relatively low resistance and having an inherent inductive reactanoe. F or example, the leads 37 and 39 may comprise a few inches of copper wire of a size suificient to carry the current through the arc discharge device 14.

A switching device, such as a hydrogen thyratron 30, for example, is connected between ground and the terminal 28 of the arc discharge device 14 to reduce the voltage at the terminal 28 to substantially ground potential when the normal-1y non-conductive thyratron 30 is fired. The anode terminal 32 of the thyratron 30 is connected to the terminal 28, and the cathode terminal 34 of the thyratron 30 is connected to ground. A capacitor 36 is connected between ground and the lead 37. The capacity of the capacitor 36 is relatively much smaller than that of the capacitor 12.

The operation of the discharge circuit 10 will now be described: The capacitors 12 and 36 are charged by the power supply through the resistor 16. Capacitor 36, connected between ground and the lead 37, is charged to a greater voltage than the capacitor 12 connected across the arc discharge device 14. The voltage across the charged capacitor 12 is smaller than the break-down voltage of the arc discharge device 14. A positive-going triggering pulse, from any suitable, conventional source (not shown in detail), is applied to the grid 38 of the thyratron 30 to trigger it into conduction. This action reduces the volt- 3 age at the terminal 28 of the arc discharge device 14 to substantially ground potential with a pulse whose leading edge is substantially vertical. The sharp drop in voltage is caused by the fast rise time of the pulse provided by the fired thyratron 30. The negative-going voltage of the pulse at the terminal 28 causes a voltage to be self-induced across the lead 39 due to its inherent inductive reactance. This voltage adds to the voltage across the capacitor 12 in proper polarity to provide a combined voltage of sufficient amplitude and proper polarity to trigger the arc discharge device 14 into conduction. The charged capacitor 36, connected in parallel with a discharge device 14 and thyratron 30, supplies a current and a voltage sufficient to insure the conduction of the arc discharge device 14. When the arc discharge device 14- conducts, the capacitor 12 discharges substantially through the arc discharge device 14 only. Thus, the thyratron 30 may be a relatively lower power handling component than the arc discharge device 14 because the capacitor 12 does not discharge through the thyraton 3t In order to trigger the arc discharge device 14 into conduction, the power supply must be capable of producing an output voltage, between the output terminals 22 and 24, that is greater than the brealedown voltage of the arc discharge device 14. Since some are discharge devices have break-down voltages in the order of thousands of volts, the power supply for the circuit must be capable of producing even higher voltages. The large capacity capacitor 12 must also be insulated for high voltage in the circuit 10.

Referring, now, to FIG. 2, there is shown a discharge circuit 50 utilizing a discharge device 14a that has a break-down voltage that is greater than the voltage output of a power supply between positive and negative terminals 22a and 24a, respectively. A capacitor 120 has one side connected directly to the grounded, negative output terminal 24a of the power supply, and the other side connected to the positive terminal 22a of the power supply through a charging resistor 16a. The capacitor 12a is also connected to the terminals 26a and 28a of the device 14a through low resistance leads 37a and 39a. The capacitor 12a is charged to a voltage below the break-down voltage of the arc discharge device 14a.

Means are provided to trigger the arc discharge device 14a into conduction by a pulse whose amplitude is sutficient, when added to the voltage across the charged capacitor 12a, to exceed the break-down voltage of the arc discharge device 14a. To this end, the anode terminal 32a of the thyratron 3th is coupled to the terminal 28a through a coupling capacitor 52. The cathode terminal 34a of the thyratron 30a is connected to ground.

The thyratron 30a may be energized either from the same power supply that provides the voltage between the positive and negative output terminals 22a and 24a, respectively, of that power supply, or by a separate power supply. Thus, positive and negative output terminals 22b and 24b, respectively, may represent output terminals that are either connected in parallel with the terminals 22a and 24a, respectively, or output terminals of an independent power supply. In either case, the negative output terminal 24b is connected to the common connection to which the negative terminal 24:: is connected. A capacitor 36a has one side connected directly to the negative terminal 24b, and the other side connected to the positive terminal 22b through a resistor 16b for charging purposes. The anode terminal 32a is connected to the common junction between the capacitor 36a and the resistor 16b through a load resistor 54.

The operation of the discharge circuit 50 will now be described: The capacitors 12a and 36a are charged through resistors 16a and 1612, respectively. The voltage across the charged capacitor 12a is below the break-down voltage of the arc discharge device 14a. A positivegolng voltage from any suitable, conventional voltage source applied to the grid 38a of the thyratron 30a triggers the normally cut-off thyratron 30a into conduction. This action causes a sharply negative-going pulse at the anode terminal 32a. This pulse has a waveform 56 whose leading edge 58 is substantially vertical. The Waveform 56 starts at a voltage of +V, the voltage of the power supply, and drops to substantially zero, or ground. This pulse is transmitted through the normally charged capacitor 52 to the terminal 28a of the arc discharge device 14a. Since the terminal 28a is also at substantially ground potential before the conduction of the thyratron fitia, the negative-going pulse from the thyratron 30a causes the terminal 28a to go from substantially zero volts to a voltage of substantially V. The voltages +V and V may be substantially equal to each other in amplitude, but opposite in polarity. The pulse at the terminal 28a has a waveform 60 whose leading edge 62 has a substantially vertical rise time. It is this very fast rise time that causes a voltage to be self-induced in the inherent inductive reactance of the lead 39a. The voltage at the terminal 28a, therefore, drops from ground potential to the voltage V. This latter action triggers the arc discharge device 14a into conduction. Once the device 14a is triggered, the capacitor 12a discharges through the discharge device 14a. Thus, substantially all of the energy from the capacitor 12a is dumped into the arc discharge device 14a. Since substantially none of the current through the .arc discharge device 14a flows through the thyratron 30a, the thyratron 30a may be a relatively lower power handling component than the arc discharge device 14a.

Let it be assumed, for example, that the break-down voltage of the arc discharge device 14a is 7 kv. (kilovolts). Let it also be assumed that the power supply between H the terminals 22a and 24a has an output voltage of only 5 kv. Under these circumstances, the pulse provided by the triggered thyratron 30a must be at least 2,000 volts to trigger the arc discharge device 14a into conduction, assuming the capacitor 12a has a full charge of 5 kv. The required triggering pulse may be supplied easily by a power supply whose output voltage is 5 kv. between the terminals 22b and 24b. Hence, either a single power supply or two separate power supplies may be used for the discharge circuit 50 of FIG. 2.

Where it is desired to send large amounts of energy through a load in addition to the arc discharge device 140, the load may be placed in series with the large capacitor 12a and the arc discharge device 14a. Referring, now, to FIG. 3, there is shown a load 64 which comprises a metal 66, such as silver, gold, and aluminum, for example, adapted to be evaporated or exploded when a large pulse of current flows through it. The metal 66 is connected in series with the capacitor 12a and the arc discharge device 14a. It will now be understood that a large pulse of current flows through the metal 66 when the arc discharge device 14a is triggered into conduction in the manner described for the operation of the circuit 50 of FIG. 2. The current through the metal 66 can be made large enough to cause it to evaporate and even to explode. The metal vapor resulting from this process is useful in coating materials in the electronic and other arts.

From the foregoing description, it will be apparent that there have been provided, in accordance with the present invention, improved discharge circuits for supplying a load with a relatively large pulse of current while employing triggering devices that utilize relatively smaller currents. While the discharge circuits of the present invention have been shown in diagrammatic form, various components useful therein, as well as variations in the circuits themselves, all coming within the spirit of this invention, will, no doubt, readily suggest themselves to those skilled in the art. For example, the hydrogen thyratron 30a may be replaced by other switching devices, such as a mercury pulser and the like, to provide suitable triggering pulses for triggering the arc discharge device. Hence, it is desired that the foregoing shall be considered merely as illustrative and not in a limiting sense.

What is claimed is:

l. A circuit for discharging a capacitor through a normally non-conductive discharge device having two terminals connected in circuit, said discharge device having a predetermined break-down voltage, said circuit having positive and negative terminals for receiving a unidirectional voltage therebetween, means connecting said capacitor between said positive and negative terminals to charge said capacitor from said voltage, relatively low resistance means connecting said capacitor between said terminals of said discharge device, at least one of said low resistance means having inductive reactance and being connected to one of said terminals of said discharge device, and means including a normally nonconductive switching device connected between a terminal of said source of voltage and said one terminal of said discharge device to cause to be self-induced in said low resistance means having inductive reactance, when said switching device is rendered conductive, a triggering voltage having a waveform whose rise time is substantially zero, said one terminal of said discharge device being connected to said negative terminal through said low resistance means having inductive reactance, and said triggering voltage being sufficient to cause said discharge device to conduct when added to the voltage across said capacitor in a charged state.

2. In a circuit for discharging a capacitor through a discharge device having two terminals connected in said circuit, said discharge device having a predetermined break-down voltage, the combination therewith of positive and negative terminals for receiving a unidirectional power supply therebetween, means connecting said capacitor between said positive and negative terminals to charge said capacitor, relatively low resistance means connecting said capacitor between said terminals of said discharge device, at least one of said low resistance means having inductive reactance, said means having inductive reactance being connected to one of said terminals of said discharge device, and means including a normally nonconductive switching device connected between said negative terminal and said one of said terminals of said discharge device to cause to be self-induced in said means having inductive reactance, when said switching device is rendered conductive, a triggering voltage having a waveform whose rise-time is substantially zero, said one terminal of said discharge device being connected to said negative terminal through said low resistance means having inductive reactance, the output voltage of said power supply being smaller than said break-down voltage, and said triggering voltage being sufiicient to cause said discharge device to conduct when added to the voltage across said capacitor in a charged state.

3. A circuit comprising a pair of terminals for applying a source of voltage therebetween, a normally nonconductive discharge device having two terminals connected in said circuit, a switching device having at least two terminals, means connecting one of said terminals of said switching device to one of said terminals of said discharge device, means connecting the other of said terminals of said switching device to one of said terminals of said source of voltage, means connecting the other terminal of said discharge device to the other of said terminals of said source of voltage whereby a voltage appears across said switching device, a first capacitor, means connecting said first capacitor between said terminals of said source of voltage to charge it, means connecting said first capacitor to said other terminal of said dischange device and said other terminal of said switching device to discharge it through said discharge device and said switching device when said switching device is actuated, a second capacitor, low resistance means connecting said second capacitor between said terminals of said discharge device, at least one of said low resistance means having inductive reactance, said means having inductive react ance being connected to said one terminal of said discharge device, and means connecting said second capacitor to said source of voltage to charge said second capacitor to a lower volt-age than said first capacitor, whereby said voltage across said switch drops sharply to Zero when said switch is closed thereby causing a voltage to be self-induced across said means having inductive reactance, said self-induced voltage when added to said voltage across said second capacitor causing said discharge device to conduct, said voltage across said first capacitor insuring conduction of said discharge device.

4. A circuit comprising a pair of terminals for a source of voltage, a voltage divider connected between said terminals, a two-terminal discharge device and a switching device having at least two terminals, means connecting one of said terminals of said discharge device to one of said terminals of said switching device, means connecting the other of said terminals of said switching device to one point on said voltage divider, means connecting the other terminal of said discharge device to another point on said voltage divider, a first capacitor, means connecting said capacitor between different points on said voltage divider to be charged by said voltage source and to be discharged through said switching device and said discharge device when said switching device is closed, a second capacitor having a relatively much higher capacity than said first capacitor, a pair of conductive means connecting said second capacitor in shunt with said discharge device, at least one of said conductive means having inductive reactance, said inductive re-actance means being connected to said one terminal of said switching device, said switching device being connected in series with said second capacitor, and means connecting said second capacitor to two additional points of said voltage divider for charging said second capacitor to a lower voltage than said first capacitor.

5. A circuit for causing a first capacitor to discharge through an arc discharge device when said are discharge device is caused to are, said are discharge device having only two terminals connected in said circuit, said circuit comprising a first and a second pair of output terminals for a first and a second power supply, respectively, means connecting one of said output terminals of each of said first and second power supplies together, a second capacitor, means connecting said second capacitor between said output terminals of said first power supply to charge said second capacitor, a switching device having at least two terminals, means connecting said switching device across said second capacitor to discharge said second capacitor when said switching device is actuated, means connecting said first capacitor between said output terminals of said second power supply to charge said first capacitor, low resistance leads connecting said are discharge device in shunt with said first capacitor, and capacitive means connecting said switching device to one of said terminals of said are discharge device to cause said are discharge device to are when said switching device is actuated.

6. A circuit for causing a first capacitor to discharge through an arc discharge device when said arc discharge device is caused to are, said circuit comprising a first and a second pair of output terminals for a first and a second power supply, respectively, means connecting one of said output terminals of each of said first and second power supplies together, a second capacitor, means connecting said second capacitor between said output terminals of said first power supply to charge said second capacitor, a switching device having at least two terminals, means connecting said switching device across said second capaci tor to discharge said second capacitor when said switching device is actuated, means connecting said first capacitor between said output terminals of said second power supply to charge said first capacitor, means connecting said are discharge device in shunt with said first capacitor, and

capacitive means connecting said switching device to said are discharge device to cause said are discharge device to arc discharge device having only two terminals connected in said circuit and a predetermined break-down voltage,

the combination therewith of positive and negative terminals for receiving a power supply therebetween, inductive reactance means having low resistance connecting one terminal of said are discharge device and one side of said capacitor to said negative output terminal, low resistance means connecting the other terminal of said are discharge device to the other side of said capacitor, means connecting said other side of said capacitor to said positive terminal to charge said capacitor to a voltage less than said break-down voltage, and means connected to said one terminal of said arc discharge device to cause a negativegoing voltage having a waveform with a substantially vertical leading edge to be self-induced in said inductive reactance means, the sum of the amplitudes of said applied voltage and said voltage across said capacitor being greater than said break-down voltage, whereby to cause said are discharge device to arc and said capacitor to discharge therethrough.

8. A circuit for discharging a capacitor through a normally nonconductive two-terminal discharge device, said circuit comprising a source of voltages having a point of voltage reference, means connecting said capacitor to said source to charge said capacitor, a first means for connecting one terminal of said capacitor to a first terminal of said device, said means having inductive reactance and low resistance, a second means for connecting the other terminal of said capacitor to a second terminal of said device, and switching means including a normally nonconductive switch connected between said first terminal 4 of said device and said point of voltage reference, a

voltage being applied across said switch by said source, whereupon conduction of said switch said voltage across said switch drops sharply to zero causing a voltage to be self-induced across said first means connecting said capacitor to said device, said self-induced voltage when added to said voltage across said capacitor causing said device to conduct.

9. A circuit for discharging a capacitor through a normally nonconductive two-terminal discharge device, said circuit comprising a source of voltages having a grounded terminal, means connecting said capacitor to said source to charge said capacitor, a first means for connecting a terminal of said capacitor to said first terminal of said device, said means having inductive reactance and low resistance, a second means for connecting the other terminal of said capacitor to said second terminal of said device, and means for switching, including a normally nonconductive switch, said means for switching being connected between said first terminal of said device and said grounded terminal of said source of voltages, said switch having a voltage applied thereacross with respect to said grounded terminal by said source whereby upon conduction of said switch, said voltage across said switch drops sharply to zero causing a voltage to be self-induced across said first means connecting said capacitor to said device, said self-induced voltage when added to said voltage across said capacitor causing said device to conduct.

References Cited by the Examiner UNITED STATES PATENTS 2,391,225 12/1945 Clark 315237 2,417,489 3/1947 Hasler et al. 315*237 2,485,037 10/1949 Clark 315-241 2,574,655 11/1951 Panofsky et al. 3l5241 X 2,795,738 6/1957 Holliday 315-241 X 2,967,975 1/196'1 Hartman 315-24'1 2,979,640 4/ 1961 Edmonson 3 l5-24l JOHN W. HUCKERT, Primary Examiner.

J. D. KALLAM, R. F. POLISSACK, Assistant Examiners. 

1. A CIRCUIT FOR DISCHARGING A CAPACITOR THROUGH A NORMALLY NON-CONDUCTIVE DISCHARGE DEVICE HAVING TWO TERMINALS CONNECTED IN CIRCUIT, SAID DISCHARGE DEVICE HAVING A PREDETERMINED BREAK-DOWN VOLTAGE, SAID CIRCUIT HAVING POSITIVE AND NEGATIVE TERMINALS FOR RECEIVING A UNIDIRECTIONAL VOLTAGE THEREBETWEEN, MEANS CONNECTING SAID CAPACITOR BETWEEN SAID POSITIVE AND NEGATIVE TERMINALS TO CHARGE SAID CAPACITOR FROM SAID VOLTAGE, RELATIVELY LOW RESISTANCE MEANS CONNECTING SAID CAPACITOR BETWEEN SAID TERMINALS OF SAID DISCHARGE DEVICE, AT LEAST ONE OF SAID LOW RESISTANCE MEANS HAVING INDUCTIVE REACTANCE AND BEING CONNECTED TO ONE OF SAID TERMINALS OF SAID DISCHARGE DEVICE, AND MEANS INCLUDING A NORMALLY NONCONDUCTIVE SWITCHING DEVICE CONNECTED BETWEEN A TERMINAL OF SAID 